1. Field of the Invention
The present invention generally relates to an attachment assist device to assist attachment of a retractable unit to a main body, a sheet feeder including the same, and an image forming apparatus including the same.
2. Discussion of the Background Art
In general, electrophotographic image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction devices including at least two of those functions, include a reading unit to read image data of documents, an image forming unit to form images on sheets of recording media according to the image data ready by the reading unit, and a sheet feeder to feed the sheets to the image forming unit. The image forming unit includes an optical writing device to direct a writing light (i.e., a laser beam) onto a surface of an image carrier (i.e., a photoconductor), thus forming an electrostatic latent image thereon, and a development device to develop the latent image with toner. In multicolor image formation, the image forming unit forms cyan, magenta, yellow, and black toner images on a single photoconductor or respective photoconductors, which are transferred therefrom and superimposed one on another on the sheet, thus forming a multicolor image on the sheet.
Image forming apparatuses further include a sheet tray that can contain multiple sheets and be retracted into and pulled out from a main body. For example, the sheet feeder includes a pickup roller to feed the sheets contained in the sheet tray to the image forming unit sequentially from the top. When the sheet tray is empty or when users desire to change a sheet size or the like, the user pulls the sheet tray out of the main body, fills the sheet tray with sheets, and then pushes the sheet tray back into the main body.
In such image forming apparatuses, if the sheet tray is not properly positioned in the sheet feeder or main body in a direction in which the sheet tray is properly inserted into the main body (hereinafter “insertion direction”), the image forming apparatus can form a substandard image on the sheet, with the image deviating from the center of the sheet in a width direction of the sheet. However, when the sheet tray is too heavy, the user has to press the sheet tray with greater force to insert the sheet tray into the sheet feeder. Yet, if the user pushes the heavy sheet tray with excessive force, the sheet tray might hit the sheet feeder, impacting the sheet tray as well as the sheet feeder. The impact to the sheet tray can disturb the sheets stacked in the sheet tray and damage the sheet tray.
In view of the foregoing, several approaches described below have been tried to assist attachment of the sheet tray into the apparatus, in particular, insertion of the sheet tray into the main body of the apparatus.
For example, JP-2006-151687-A discloses an image forming apparatus that includes an engagement pin provided in the sheet tray, a drawing mechanism to draw the sheet tray into the main body, and a guide groove formed in the main body to guide the engagement pin, thus guiding insertion of the sheet tray into the main body. The drawing mechanism includes a toggle spring and a pivotable arm to engage the engagement pin provided in the sheet tray. Additionally, the guide groove includes a linear portion in parallel to the insertion direction of the sheet tray and a bent portion bent toward a pivot point of the pivotable arm.
With this configuration, when the pivotable arm pivots to a predetermined position with the engagement pin engaged with the pivotable arm and guided by the guide groove, the drawing mechanism pulls the sheet tray via the engagement pin with the bias force exerted by the toggle spring. Additionally, when the engagement pin is guided by the bent portion of the guide groove bent toward the pivot point of the pivotable arm, the pivotable arm can pivot easily with the bias force of the toggle spring.
Additionally, for example, JP-2007-70068-A discloses a velocity-dependent damper unit to adjust a load for decelerating movement of the sheet tray according to a velocity with which the sheet tray is drawn by the bias force of the toggle spring. Thus, fluctuations in the velocity of the movement of the sheet tray can be reduced.
Although such an arrangement has advantages, it also has several drawbacks.
For example, because the sheet tray should be pulled into the main body against various resistive forces acting on the sheet tray, using the damper unit can increase the force required for pulling out the sheet tray from the main body. Examples of such resistive forces include sliding resistance due to the weight of sheets contained in the sheet tray, frictional resistance in positioning the sheet tray, and resistance of a sheet feed mechanism being engaged or disengaged from the sheet tray.
At present, barrier-free facilities have been promoted to provide easier access for elderly people and people with disabilities, and, in December 2000, the U.S. government released Section 508 of the Rehabilitation Act, specifying standards for accessibility. More specifically, Section 508 specifies that the maximum force required to activate controls and keys operated mechanically shall be 5 lbs. (22.2 N). Therefore, the increase in the force to pull the sheet tray should be limited, and thus it is important to reduce the resistance in insertion of the sheet tray while increasing efficiency in insertion of the sheet tray.
The above-described problem is not limited to drawing the sheet tray but is also present in drawing any retractable unit, such as a duplex unit for forming images on both sides of sheets, that is closably openable relative to the main body of the image forming apparatus.
Therefore, the inventors of the present invention recognize that there is a need for an attachment assist device capable of positioning the retractable unit properly at a predetermined position in the main body as well as drawing the retractable unit into the main body efficiently.